Phosphorodithioate salts for atf fluids

ABSTRACT

ALKALI AND ALKALINE EARTH METAL SALTS (ATOMIC NOS. 3 TO 20) OF O,O-DI(STRAIGHT CHAIN ALKYLPHENYL) PHOSPHORDITHIOATES, WHEREIN THE ALKYL GROUPS ARE OF FROM 8 TO 30 CARBON ATOMS, ARE USED IN AUTOMATIC TRANSMISSION FLUIDS AS FRICTION AGENTS.

United States Patent 3,630,918 PHOSPHORODITHIOATE SALTS FOR ATF FLUIDS Bruce W. Hotten, Orintla, and Thomas V. Liston, Kentfield, Calif., assignors to Chevron Research Company, San Francisco, Calif. No Drawing. Filed Mar. 29, 1968, Ser. No. 717,381 Int. Cl. C09k 3/00; C10m 1/48 U.S. Cl. 252-75 9 Claims ABSTRACT OF THE DISCLOSURE Alkali and alkaline earth metal salts (atomic Nos. 3 to 20) of- 0,0-di(straight chain alkylphenyl) phosphorodithioates, wherein the alkyl groups are of from 8 to 30 carbon atoms, are used in automatic transmission fluids as friction agents.

BACKGROUND OF THE INVENTION Field of the invention Numerous additives are included in automatic transmission fluids to improve the friction and lubricating properties of the fluids. Two important functions of additives are to prevent oxidation of the oil which leads to sludge and lacquer formation and to improve the frictional properties between the clutch plate. The presence of the sludge or lacquer on the surface of the discs used in the automatic transmission will frequently cause what is known as stickslip. This phenomenon is brought about by the fiber composition on one of the discs momentarily grabbing the steel disc, then momentarily slipping on the surface of the disc, only to instantaneously grab the steel disc again. Because of this effect, an interrupted motion is transmitted to the passengers in the vehicle. Sludge and lacquer deposition can be significantly inhibited by effective oxidation inhibitors and detergents.

Additives are also included in the oil to reduce the low speed friction between the clutch plate surfaces. It is found that an increase in the coefficient of friction with a decreasing clutch plate sliding speed will result in stickslip action of the clutch plates and, therefore, undesirable shift performance. Severe stick-slip results in audible squawk and sometimes transmission failure. Cf. Rodgers and Haviland, Friction of Transmission Clutch Materials as Affected by Fluids, Additives and Oxidation, 194A, P-reprint for the SAE Meeting of June -10, 1960. Desirably, therefore, at low speeds, the coefiicient of friction should not decrease with decrease in sliding speed.

Because temperatures can be quite severe in the area of the clutch plates and automatic transmission fluids are relatively infrequently changed, it is necessary that additives have good thermal and chemical stability for long periods of time. It is not enough that the additives provide good performance in a single short-term test, but the additives must remain effective over long periods of time.

Description of the prior art U.S. Pat. No. 3,175,976 teaches a combination of zinc (mixed dialkyl) dithiophosphate with an alkyl methacrylate-vinyl pyrrolidone copolymer in automatic transmission fluids. Alkali and alkaline earth metal salts of phosphorodithioates are taught in a number of patents for a variety of purposes. See, for example, U.S. Pat. Nos. 2,365,938, 2,529,304 and 2,600,154. The various salts are taught for anti-corrosion and extreme pressure properties and as anti-oxidants.

SUMMARY OF THE INVENTION Automatic transmission fluids are provided having an elfective amount, for inhibiting oxidation and improving the frictional properties of the fluid, of alkali and alkaline 3,630,918 Patented Dec. 28, 1971 to the phenyl group at an internal or terminal carbon atom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Phosphorodithioate additives The phosphorodithioate additives used in this invention will, for the most part, have the following formula: s

M(s f wnin wherein M is an alkali or alkaline earth metal of atomic Nos. 3-20 (lithium, sodium, potassium, magnesium or calcium), n is a number of from 1 to 2 and equal to the valence of M, Ar is a phenylene group and R is a straight chain alkyl group (free of unsaturation) of from 8 to 30 carbon atoms, having either terminal or internal attachment to the phenyl ring. In any one molecule, the Rs may be the same or different and may be a single alkyl group or a mixture of alkyl groups. Preferred alkyl groups are those having an average number of carbon atoms of at least 12 and not greater than 28, more usually of from about 15 to 25. R may be attached to the ortho, meta or para positions but will usually be attached predominantly to the ortho and para positions.

A preferred alkyl group source is cracked wax olefins or polyethylenes obtained by the polymerization of ethylene using an alkyl aluminum catalyst. The most desirable fractions are those having an average of from 15 to 25 carbon atoms.

Illustrative phosphorodithioate radicals which may be used with any of the specified metal cations to form salts are 0,0-di(undecylphenyl) phosphorodithioate, 0,0-di (octadecylphenyl) phosphorodithioate, O,O-di(C cracked wax olefin derived alkylphenyl) phosphorodithioate, O,O-di(C polyethylene derived alkylphenyl) phosphorodithioate, etc.

The phosphorodithioic acid metal salt compositions are readily prepared according to known procedures. Alkylation of phenol with olefins is a well-known reaction. The formation of phosphorodithioic acid esters is achieved by the reaction of phosphorus pentasulfide with the desired phenol in the appropriate proportions at elevated temperatures. The resulting phosphorodithioic acid ester may then be reacted wtih a basic reacting metal salt or hydroxide. For example, the carbonate or acetate can be conveniently used.

Automatic transmission fluids The automatic transmission fluids generally have a viscosity in the range of from about to 1,000 SSU (Saybolt Seconds Universal) at F. and from about 35 to 750 SSU at 210 F. The base oils for the automatic transmission fiuids are light lubricating oils and ordinarily have a viscosity in the range of about 50 to 400 SSU at 100 F. and 33 to 50 SSU at 210 F. The base stock is a lubricating oil fraction of petroleum, either naphthenic or paraflinic base, unrefined, acid refined, or solvent refined as required in the particular lubricating need. Also, synthetic oils may be used as the base stock having the necessary viscosity requirements.

The phosphorodithioates used in this invention will generally be present in the automatic transmission fluid in from about 0.05 to 3 weight percent, more usually in from about 0.1 to 2 Weight percent. They may also be used as concentrates wherein the phosphorodithioate may be present in from about 5 to 25 weight percent.

The automatic transmission fluids will normally have a large number of other additives present. Automatic transmission fluids are usually heavily compounded oils.

Included in the oils are detergents, including neutral, mildly overbased and heavily overbased detergents. These detergents include acrylate-vinyl pyrrolidone polymers, alkenylsuccinimides of alkylene polyamines, mildly basic mahogany sulfonate salts, mildly basic carboxylate salts, and more heavily overbased sulfonate and carboxylate salts.

Also included in the oil are viscosity index improving agents which are normally high molecular weight polymers, such as the acrylate polymers, and hydrocarbon polymers, such as polyisobutylene or ethylene/ propylene copolymers.

The detergents will normally be present in from about to 500 mm./kg. of the base oil. The viscosity index improver will normally be present in from about 0.5 to percent by weight of the base oil.

Other additives include pour point depressants, antifoam agents, additional anti-oxidants, additional antisquawk agents, etc. Numerous automatic transmission fluid additives are listed in U.S. Pat. Nos. 3,156,652 and 3,175,976, whose disclosure is incorporated herein by reference.

EXAMPLES The following examples are offered by way of illustration and not by way of limitation.

Example A Preparation of alkylphenyl phosphorodithioic acid.- Into a reaction vessel was introduced 469 g. of alkylphenol prepared by the alkylation of phenol with C1848 polyethylene (av. mol. wt. 469; hydroxyl No. 120) and 222 g. of phosphorus pentasulfide. The mixture was heated to 160 C. and maintained between 150 and 160 C. for 7 hours. The mixture was then blown with nitrogen, leaving the product which weighed 490 g.

Analysis.-(percent): S, 4.5, 4.4; P, 2.9; O, 4.9; Acid No.: 42 mg. KOH/ g.

Example I Into a reaction flask was introduced 100 g. of 0,0-di (C cracked wax olefin derived alkylphenyl) phosphorodithioic acid (Analysis: percent P, 3.3; percent 0, 5.7; Acid No.: 54 mg. KOH/g.), and 6.4 g. of a 40 weight percent solution of potassium hydroxide in methanol. The temperature was then slowly raised to 120 C., distilling off the methanol. At the end of this time, the product had a pH of from about 6 to 7.

AnaIysis.Mol. wt. (ThermoNAM)=1030; percent S, 5.68; percent K, 5.7.

Example II Into a reaction vessel was introduced 102 g. of the phosphorodithioic acid described in Example I and 5.3 g. of sodium carbonate and the mixture rapidly stirred with heating. The temperature was slowly raised to 120 C. At the end of this time, the mixture was allowed to cool and the product analyzed by infrared spectrum.

Example III Into a reaction vessel was introduced 58 g. of the phos phorodithioic acid described in Example I and 10 g. of calcium acetate monohydrate and the mixture stirred and heated at 110 to 120 C. The temperature was maintained for 3 hours and 15 minutes, distilling off the acetic acid as formed and continuously sparging the reaction mixture with nitrogen. The product was then isolated.

AnaIysz's.Percent Ca, 3.6 (calcd 3.8); percent P, 3.1 (calcd 3.0).

Example IV Into a reaction vessel was introduced 102 g. of the phosphorodithioic acid described in Example I and 10.8 g. of magnesium acetate tetrahydrate. The solution was stirred while slowly raising the temperature to 75 C., the mixture forming a porous solid. A vacuum was applied to the mixture while sparging with nitrogen and the product then isolated.

Analysis-Percent S, 4.3.

Example V Into a reaction vessel was introduced 10.3 g. of di (PE alkylphenyl) phosphorodithioic acid (PE polyethylene of from 18 to 28 carbon atoms supplied by Gulf Chemical Co.) (Percent P, 2.9; percent S, 4.5, 4.4; Acid No.: 42 mg. KOH/g.), 0.7 g. of a 40 weight percent solution of methanolic potassium hydroxide and a mixture of methanol and methyl ethyl ketone. The mixture was stirred and heated on a hot plate and then blown with nitrogen while heating on a steam plate. The product was then isolated.

Example VI Into a reaction vessel was introduced 102 g. of the phosphorodithioic acid described in Example I and 7.4 g. of lithium carbonate and the mixture heated at C. for about 8 hours, followed by filtering while still hot. The product was analyzed by its infrared spectrum and elemental analysis for lithium. Percent Li, 0.43.

In order to test the frictional properties of the phosphorodithioic acid salts used in this invention, the salts were compounded at 1 weight percent in a base oil consisting of 80 weight percent of a California naphthenic base oil having a viscosity of about 38 SSU at 210 F. and 20 weight percent of a California paraffinic base oil having a viscosity of about 42.5 SSU at 210 F.

The following data show the sliding friction properties of the ATE fluids of this invention. These data were obtained by taking a piece of a commercial clutch plate facing (a compressed composition paper) and testing it under the temperature and velocity conditions in a lowload friction apparatus. The apparatus employs a rotating steel disc of the type found in automatic transmissions. The fluid tested surrounded the disc, while the clutch facing material was held against the disc under a constant load. The test method is similar, with minor variation, to the method described by Haviland et al., Lubrication Engineering, 17, No. 3, March 1961. As hereinafter disclosed, the test results correlate with the results obtained in standard test transmissions under actual driving conditions.

Experience has shown that in an acceptable fluid, the coeflicient of friction should decrease as the rubbing speed decreases at any given temperature. The coefficient of friction is determined at the velocity and temperature conditions set forth in the table. The coeflicient of friction should not exceed about 0.18 at low rubbing speeds or grabbing and squawk will occur. At the same time, the coefiicient of friction should be greater than about 0.06 or slipping and flare will occur. The designation f.p.m. signifies feet per minute.

TABLE I Sliding coclt. of friction at Phosphorodithioie Temp. 0 5 20 acid salt additive F. f.p.m. 1'.p.m. l.p.1n.

75 0. l0 0. 17 0. 17 I K(0\VO15-3(] alkyl phenyl) 0. 10 0. 13 0. 14 300 0.11 0.11 0. 13 75 0. 16 0. l7 0. 17 II N3.(0W015-2n alkylphenyl) 175 0. 08 0. 12 0. 13 300 0. O6 0. 10 0. 11 75 0. 17 0. l8 0. 18 III Ca(0W015-:o a1ky1pheuy1) 176 0.13 0. 16 0. 16 300 0. 08 0. l3 0. 14 75 0. 15 0. 17 0. 17 IV Mg(cwo alkylphenyl).-. 175 0. 12 0. 16 0. 16 300 0. 09 0. 14 0.15 75 0. 15 0. 17 0. 17 V K(PE18-zs alkylphenyl) 175 0.07 0. 10 0. 11 300 0. O6 0. 08 0. 08 75 0. 14 0. 17 0. 17 VI L1(e\\'015-m alkylphenyl) 175 0. 08 0.13 0.14 300 0. 07 0. l1 0. l2 75 0. 24 0. 18 0. 17 Base 011 175 0.25 0.20 0.20 300 0. 30 0. 28 0. 26

e\vo g g =alkyl groups on phenol derived from GIL--20 cracked wax olefin fractlon; P Ema ullryl groups on phenol derived from C15 :a polyethylene fraction.

A further test was carried out using the apparatus described above. In this test, the static measurement is obtained. The apparatus is started and run at 36 rpm.

for 30 sec, The rheostat control of the motor is quickly turned ofi and the rider holder is moved away from the strain gauge. The curve obtained should appear as a square wave. With poor frictional materials, long tails referred to as rooster tails may be obtained as momentary grabbing occurs initially or when the apparatus comes to a complete halt. With the compositions of this invention, almost no rooster tail is observed, either initially or at the end.

It is evident from the above results the compositions of this invention show good friction properties over a wide range of temperatures. They will also demonstrate good stability under severe conditions, since the alkylphenyl esters are known to have superior stability to the alkyl esters. The automatic transmission fluids of this invention can, therefore, be used for long periods of time while retaining the desirable frictional and oxidative properties.

As will be evident to those skilled in the art, various modifications on this invention can be made or followed, in the light of the foregoing disclosure and discussion, Without departing from the spirit or scope of the disclosure or from the scope of the following claims.

We claim:

1. An automatic transmission fluid having as a base oil a major amount of a hydrocarbon light lubricating oil containing 0.05 to 3 weight percent of an additive having the following formula:

- 6 wherein M is an alkali or alkaline earth metal of atomic Nos. 3-20, Ar is a phenylene group, R is a straight chain alkyl group of from 8 to 30 carbon atoms and n is 1 or 2 and equal to the valence of M.

2. A composition according to claim 1, wherein M is potassium.

3. A composition according to claim 2, wherein R is a straight chain alkyl group of from 15 to 20 carbon atoms.

4. A composition according to claim 1, wherein M is sodium.

5. A composition according to claim 1, wherein M is magnesium.

6. A composition according to claim 1, wherein M is calcium.

7. A composition according to claim 1, wherein M is lithium.

8. A composition according to claim 1, wherein R is a mixture of straight chain alkyl groups of even number of from 18 to 28 carbon atoms.

9. A composition according to claim 1, wherein said automatic transmission fluid has, as its base oil, a light lubricating oil having a viscosity at 100 F. in the range of to 400 SSU.

References Cited UNITED STATES PATENTS 3/1965 Foehn 252 6/1968 Lyle et al. 252-32.7 E

US. Cl. X.R. 

